Methods of producing an ophthalmic lens, particularly as corrective eyewear, generally include first obtaining or removing a suitable right and/or left ophthalmic lens blank from a source of semi-finished products, such as a product store. The term “semi-finished” is used to mean that the ophthalmic lens blanks, which are usually round or oval in plan view, have not yet been edged, and have already been machined or in another way contoured on one of their two optically active faces.
Further machining and/or polishing operations are carried out while holding the lens blank by means of a blocking device attached to one of the faces of the lens blank while a tool operates on the opposite face of the lens blank During this treatment of the surface of the lens blank, or surfacing, the lens blank is repeatedly taken a hold of by a machine.
The lens blanks are then prepared for the blocking operation, namely by applying a suitable protective film or a suitable protective lacquer to protect the optically active face which has already been machined or contoured, i.e. the first face or blocking face.
The machinery that is used to “block” the lens typically includes a blocking support, or a grip block or chuck, a blocking means for receiving and holding a semi-finished lens blank via one of its main faces, and a means for securing the nose of various machine tools or measurement and inspection devices to provide blocking of the lens blank on the machine or the device on the opposite face of the lens blank. Typically, a block is secured onto one of the main faces of the lens blank by casting thereon a fusible molten anchoring material having a low melting temperature (or a polymeric material) in order to enable the lens blank to be subsequently mounted or anchored on the lens holder of a machine, for example, a surfacing machine, an edging machine, or a polishing machine. A suitable type of anchor or fixturing material that may provide the requisite adherence to a lens surface may be a compound having a melting point of around 117° F. (e.g., Alloy 117), comprising approximately 45% bismuth, 23% lead, 8% tin, 5% cadmium, and 19% indium.
There are several disadvantages with current blocking systems. During the blocking of an ophthalmic lens blank, there may be a large number of blocking rings that must be used, depending on the lens blank, and this is cumbersome. New blocking rings are also being frequently manufactured and added to accommodate new lens products as they become more complex. The blocking rings have to be constantly exchanged for new rings. Another problem with current blocking systems is the need for multiple inserts having different thicknesses, in order to produce a desired thickness of the blocking or anchoring material. Yet another problem with current blocking devices is that existing blocking processes are inefficient and do not allow a user to control the amount of blocking or anchoring material used per lens, thereby resulting in wasted blocking or anchoring material throughout the process.
Thus, there is a need for a simplified, cheaper, automated, and more efficient blocking apparatus and accompanying features that are capable of dynamically changing, such that changing a reference may be based on a single ring and a single insert, so that only one adjustable ring unit and one insert are needed, and that will allow the amount of blocking or anchoring material used in the process to be optimized for more efficient blocking or anchoring use and/or recycling during the blocking process.